Enamel coated articles and method of making same



R. BROWN May 27, 1952 ENAMEL COATED ARTICLES AND METHOD OF MAKING SAMEFiled Sept. 10, 1948 Patented May 27, 1952 ENAMEL COATED ARTICLES ANDMETHOD OF MAKING SAME Ralph Brown, Fall Brook, Calif., assigner toElectrical Products Corporation, Los Angeles, Calif., a corporation ofCalifornia Application September 10, 1948, Serial No. 48,708

7 Claims.

This invention relates to an enamel coated article and a method ofproducing the same. Specifically, the invention pertains to panelscapable of being secured together in side-by-side and end-to-endrelationship to produce a multipanel unit suitable for structuralpurposes, for tiling, or as a background for a sign structure, Vthepresent concept relating particularly to a method of coating the outersurfaces of the panels with vitreous enamel in a manner such that noenamel is present on the contacting edges of abutting panels so thatcracking or fracture of the hard coating, due to compression between thepanels during the assembly of the latter, is entirely avoided.

Metal panels are used quite extensively in the manufacture of signs, thepanels being assembled upon a framework and secured to the framework bybolts passing through holes in the panels. It is customary to coat theouter surfaces of the panels with paint, lacquer, pigmented enamel orother protective and ornamental coating agent of suitable color so as toprotect the sign from the elements and to afford an attractiveappearance. When a more durable and glossy finish is desired, one ormore coatings of porcelain or vitreous enamel may be applied to the signpanels and while this is frequently done, much difficulty is experienceddue to the fragility of the poreclain coating, especially when the headsof the attaching bolts exert pressure against the porcelain coatingsaround the bolt holes of the panels. Such a condition results inbreakage of the enamel so that signs incorporating porcelainized panelsfrequently have defects in the porcelain coatings, particularly adjacentthe bolt holes and at corners where the enamel is unable to resist thepressure to which it is subjected by the bolts. Such defects are usuallytouched up with paint which soon deteriorates, and the defects in theporcelain continue to increase in the same way that cracks in glasscontinue to extend.

Frequently, when sign faces are required to be larger than ispermissible through the use of conventional overlapping sheet metalplates, the edges which are to abut may be provided with flangesdisposed at right angles to the plane of the face of the plates orpanels and such panel segments may be drawn together by bolts extendingthrough holes in the abutting ilanges. In such cases, when the panelsegments have been coated with vitreous enamel which, in additionto'covering the faces of the panel segments,

covers the flanges thereof, the .pressure exerted by the attaching boltsin drawing and holding the panel segments together is suiiicient tocrack or break the vitreous enamel and such fractures or chips extendout along the enameled faces of the panel segments. For this reason, theuse of vitreous enamel as a coating on components which must be boltedor otherwise secured together has been heretofore believed quiteimpractical and, while the practice continues, signs embodying suchenamel coated components are usually imperfect as regards their outercoated surfaces, when erected on a building or other support.

It is an important object of this invention to alleviate the conditiondiscussed above by providing a method of coating sign panels, and thelike, in a manner such that the vitreous coating is deposited only onthe planar surfaces of the panel and excluded from the abutting anges sothat the latter'can be secured together without danger of cracking orchipping the enamel coating on the planar surfaces of the panels oralong the edges thereof. This object is best attained by providing theintersection of the iiange and planar surface of each panel with arelatively sharp edge or corner, and a depression in said surface spacedinwardly from the corner and extending alongside the same. By thisprovision, the vitreous enamel on the surface of the panel, actingthrough the phenomenon of surface tension or contractile surface force,acts to draw the enamel adjacent thhe edge toward the depression so asto prevent flow of the coating over the sharp edge and thus precludesany possibility of the enamel flowing onto and lodging on the side ofthe ange, particularly during the firing of the enamel coating on thepanel.

Another object of the invention is to provide a method of applying acoating of vitreous enamel to panels of the character referred to, s uchmethod consisting inv applying a bonding agent to the outersubstantially planar surface of a panel, applying one or more layers ofenamel slip to the bonding agent, preferably by a spraying operation,removing any slip which may have been deposited on the flange of thepanel during the spraying step, al1 the slip then being disposed on saidgenerally planar surface with its edges dened by the sharp cornerthereof,

and finally applying heat to the slip to cause it to flow and fill thevoids. The enamel slip, when fired, provides a continuous extremelyhard, impervious and highly ornamental coating; the yenamel disposedadjacent the sharp corner being drawn inwardly, dueto surface tension ofthe enamel, and hardening, usually in the form of a bead located inclose proximity to said corner but not extending therebeyond. By thismethod of coating articles of the character referred to, the enamelcoating is coniined to an area which does not contact portions of panelsor other components so that .the possibility -of crackingor chipping thevitreous enamel, due to compression thereof between the panels, isentirely avoided.

Another object is to provide an ornamental sign panel capable of beingjoined to -adjacent panels, the panel being preferably cast from metaland of a structural shape capable of= sustaining considerable loadwithout distortion and without the aid of separate means.

Further objects of the invention will appear from the followingspecification and fronrthe drawing, which is intended for the purposel01 illustration only and in which:

.-.Figfi-is .a .perspective View of -a typical ,flanged paneladapted foruse -as tiling or4 as acomponent of a -sign structure, the ,outerornamental surface .ofthe .panel being coated .with vitreous enamel inaccordance with the present improved .method;

c-Eig. 2. is an -enlarged cross-sectional .view throughaportion ,of thepanel, taken onf4 line zwzuoffFg.

.'.Fig.3.is a View similar .to'Fig.2 but 'showing the .panel joined toasimilar panel;

"Figs 4a, Y4I) and `lic are fragmentary crosssectional views through anenamel coated panel,

, illustrating the ,deleterious condition which .may

exist Awhenthe irregular surface of the panel. is Ycoated undercertaincircumstances, but which lcoriditionjs.desirableand utilized togreat ad- Jvantage in j thel` present method of limiting theapplicationof the enamel coating toareasjdis- .-Posed'inwardlyof theedge of the panel.

Fig. 5'I is, a view sirnilar to `Ii`ig.i'3 but showing the adjoiningedges ci panels of alternativeconi struction; and

Figfdis a. composite cross-sectional view of Vthe adjoining. edges of apair of Vmore or less l 7'conventional panels,.illustrating thedeleterious condition which exists .when no provision is madeforpreventing the coating from'flowing over the l sides orends of' .thepanels.

jAsj previously indicated,` the. present invention l` is directed tocoated. panels and other elements which` are to: be .assembled inside-by-side or end-tofend relationship. by bolts,I rivets, or otherjiastening'means. ySuch elements may take the form of tiles,.signcomponents, the walls of refrigerators, kitchen ranges, etc., theelements l) I2 projecting at right angles to the portion H.l

The outer surface of the plate-like portionll may be grooved, ribbed or.otherwise embellished toprovide any pleasing andartistic effect. In.the presentdrawing this surface is illustratedas provided with raisedbosses-or .pillows i'which may -be 1ofany-desired cross-sectionalcontour, ithaving been determined that such a pillcwed .surface providesan yabundance of light-reliectsurfaces which` cooperate ingdusing lightemanating; f rom theielectric illuminating means Atends toY fracture.

of the sign or from adjacent signs or other light sources. The flangesI2 of the panels have apertures I4 through which attaching bolts I5 areadapted to pass, as shown in Fig. 3, nuts IS being screwed onto thebolts to draw the flanges of adjacent panels together so as to maintainthe Vpanels in-A side-by-side and end-to-endv relation- `ship and thusbuild up acompletesignor building wall of desired size andconfiguration.

As previously pointed out, it is highly desirable that the exposedsurfaces of the sign wall VVbe coated.:vvitha material of suitable colorwhich Vis-hard, impervious and durable over long periods .oftime.etliese desirablecharacteristics is vitreous enamel :'whichgiis -wellrecognized as a highly eicient A coating material possessing all ofcoatingmaterial for elements which are to be exposedto variable weatherconditions and which must be'of highly ornamental character. Since thedevelopment of avitreous enamel having a y relatively ,lowV meltingpoint it .hasbecome practical to.apply such a coating ,to`aluminum,.alloy .articles such lastice sign components disclosedAherein.

. nlFigfdthere areshown theY adjoining sides -`Aof apair ofgpanela Aorsimilar elementsZB which, 'forf'the Apurpose ofillustration,.mayf beconsidered as Aof the construction Ythus' far described To apply avitreous enamel coating 2 I A.to theouter planar surfaee'z of thepanels, .thesurfaceaare "iirst Vprovided with 4a suitable .bonding.agent laiter which the enamel ffslipis superimposed-on the agent. Theslip'isusually. sprayed .thereon and .during this operation it vis .apttof` be. Ainddvertently applied to the outer Ysurfaces ,of the1ianges23. In other instances, theslipmaytend to .flow over the usuallyrounded corner. or intersection-between the surface .22 and thejlanges23 and onto the lilanges. 11n any event,',it. is

necessaryto remove any slip from4 theLiianges before firing thesame. "Ithas ,beenjoundjthat .when the slip is `subjected to heat to providejthelfiowalole vitreous enamel, the latter in. spreading outA tends to ilowfrom the surface 22over the rounded corners, onto the iianges'23asin'dicated at'23'. -In someinstances, the enamelmay merely formabead;24 which ove'rhangs the intersection-oi the Surface 22andltheanges`23.

"It is thusseen that during the ringprocess, a

portionpf the vitreous enamel'l may` harden onV the--flanges 23 orat'the corner between the planar surface and-the flanges. :Consequently,when the panels 2i) are bolted together the frangible'enamel disposedbetween the panels.is subjectedtoV considerable compression4 and thusSince the enamel coating.' is continuousy-it -is apparent that cracks orchips occurring Y-in p the Acompressed portions of the enamel mayextend` to areas of the enamelled surf-acer? which are-.adjacent to; the.anges`;23. thus impairing the protective quality ofthe coating anddetracting from the appearance of the sign wall. As previously-pointedout, to applicants knowledge, no satisfactory solution to .this problemhas heretoforebeenproposedand. for

this reason,V vitreous enamelled signs--liavegnec essarilybeen ofinferior quality.

It isfthe-aim or" the present invention toprovide a .practical solutionto the problem discussed above,4 through a method and meansbywhichvitreous enamel can be applied to sign panels` and kother elements insuch a manner that ninjury .to the glassy lcoating is entirely avoidedduring -thedrawing of the-parts together. Y, Referring vto Figs; 12:andl of the drawingfailange I2-o1` ithef'iinproved: signv panel f Ais-groundor otherwise nished on its exterior surface so as to provide asharp corner at the intersection of the flange I2 and the planar portionII.

Spaced inwardly from the sharp corner 25 and extending paralleltherewith is a depression 26. The upper surface 21 of the portion IIthat lies between the depression 26 and the corner 25 may slopedownwardly from the corner so that the included angle of the corner ismade slightly less than 90. This area 21 of the upper surface of theplate-like portion Il provides one side of the depression 26, the otherside of the depression being preferably formed by the sloping side 28 ofthe outermost pillows I3 of the panel. The depression 25 provides, ineffect, a trough, groove or channel into which a quantity of vitreousenamel can flow. The forming of the sharp corner 25 and the depression26 at the edges of the panel comprise important steps in the overallmethod of forming the enamel coated surface ofthe panel or similararticle. With a panel I0 thus fabricated, the outer surface of theplatelike portion I I is coated with vitreous enamel in the manner to benext explained.

An essential step in the method of coating the exposed surface of themetal panel I0 is that of applying to that surface a suitable bondingagent. Various agents can be advantageously employed for this purpose,and the invention is,

therefore, not limited to the use of any particular material. After thebonding agent been applied to the surface to be coated, a layer ofsemifused glassy substance 30, commonly referred to as enamel slip isapplied in a liquid state tothe bonding agent by a spraying or otheroperation. Following the deposition of the slip, any of the coatingmaterial which may have been inadvertently applied to. the outer surfaceof the ange I2 is wiped off so as to confine the material to the surfaceII which is to be coated. After the bonding agent and slip have beenapplied in the manner explained above, the slip is exposed to a heatingor firing process which, as is well known in the art, changes thecharacteristics thereof in amanner such that a flowable vitreous enamelis produced. As the coating material 30 which has a low melting point isfired, it spreads out evenly over the entire area to be coated, andduring this flowing the glassy material which is disposed on the surface28 exerts an upward pull on the enamel tending to withdraw the same fromthe depression 26. Due to this condition, the enamel on the surface 21is drawn toward the depression 26 and thus prevented from flowing overthe corner 25, the material then hardening in this condition andbecoming tenaciously bonded or fused to the metallic surface. Theprevention of the flow of the vitreous material over the corner 25 is,as above explained, attributed to the phenomenon of surface tension orthe contractile surface force due to liquiflcation of the materialduring the firing process. This results in the formation of beads at theedge ofthe enamel as shown in Figs. 2 and 3 adjacent the sharp,acute-angled corners 25.v

, The basic principle upon which -the present method of applying enamelcoatings to sign panels, or the like, is dependent, is illustrated moreor less diagrammatically in Figs. 4a, 4b and 4c. In coating theirregular outer surface 34 of a panel having a groove or flute 36 in theouter surface, the vitreous enamel is applied to the surface includingthesides 31 and bottom 3 8 of the groove and thereafter red to cause'the enamel to harden thereon. When the bottom 38 of the groove 36 isrelatively wide, the vitreous enamel 39 clings to and hardens in placeagainst the bottom and is not affected to any appreciable extent by theupward pulling force exerted by the shrinking of the enamel on thesloping sides 31 of the groove. However, it has been determined that ifthe width of the bottom 38 of the groove 36 is made relatively small,for example, equal to or. less than approximately eight times thethickness of the applied enamel coat, during the firing process thesurface tension and shrinking of the enamel on the sloping sides 31causes pulling forces tobe exerted in oppositely inclined directions andthus the enamel is drawn upwardly away from the bottom 38 as shown at 4Uin Fig. 4a. During this action, the enamel separates or breaks apart andcrawls up or, in other Words, is drawn upwardly along the sides 31 ofthe groove 36, as indicated in Fig. 4b, thus causing discontinuity ofthe enamel surface within the groove and impairing the protectiveproperties and the appearance of the coating.

The principle involved in drawing the enamel upwardly from the bottom ofthe narrow groove and causing the same to break apart, while ordinarilyleading to an inferior coating ofthe surface of the panel, is employedin my method to great advantage. It has been recognized that Vsince thepulling forceof the enamel being fired is capable of withdrawing theenamel from the bottom of the groove and causing it to break apart, thisforce can be advantageously employed for withholding the enamel coatingfrom flowing over the edge and onto the flange of a sign panel orsimilar article. It will be seenfby reference to Fig. 4c, that if thepanel 35 is cut into two parts by a vertical parting line B3 extendingthrough the center of the groove 36 then the broken edges of the enamelcoating are drawn away from this line. VThe intersection of the line 43and the bottom surface 38 of the groove 36 may be regarded as :theequivalent of the corner 25 of the present panel I0 and it is thusapparent that during the firing of the enamel coating the latter can becaused to draw away from the corner to a slight extent or at leastprevented from flowing over the corner, the extent of withdrawaldepending largely upon the surface tensions of the heated vitreousenamel. It is thus apparent that the deposition of the enamel coatingcan be. controlled with a high degree of accuracy and the coatingprevented from flowing onto areas where it might be subjected tocompression when the panels are bolted together. A

Several factors contribute to the successful coating of the externalsurface of a panel of the type referred to above. For example, bysloping the surface 21 toward the depression 26, the contractile surfaceforce, and therefore the upward pulling force, is augmented by gravitywhen the enamel is fired in a horizontal position. Moreover, by makingthe corner relatively sharp, the coating material, when in a freelyiiowable state, will not tend to flow over this corner but rather willbe retained by the material on the surface 21. In other words, thesharpcorner 25 offers resistance to the flow of material down the sideof the flange I2 and, since passage of the material overy the corner isprevented, the gravitational force which might otherwise overcome thesurface tension of the liquid material is ineffective and, theenamelremains ori:the.upper surface assai-19s ofthe panel;V Itis thusseenthat only the desired surface, tha-tis', only that surface which isexposed tolview Tand tothe Weather, is rcoated with the vitreous enameland thefiangesf I2 remain free from. undesirable coating. Consequently,when twopanels are drawn together by the bolts l5 and nuts I 6 to form amulti-panel Wall, the frangible glassy material is not subjected tocompression andthusis not damaged.

Itlhas .been determined'by-research `that the width'of thedepression-and the distance between its innermost side and the cornervis also quite important tothe success of the method; Thisdistancavwhichis representedV by the dimension character Xin Fig. 2, ispreferably not less than one-half the total thickness of the enamel andnot greater than approximately-four times the thickness of the appliedcoat, this range permitting :the use vof enamel of various thicknessesand viscosities. As an example, when the thicknessof the enamel. isapproximately .008 inch, th'edimension X may be within the range of .004inch; depending upon the viscosity of the heated vitreous enamel to beapplied. It is thus seen thatthe width of the Ysurface 21 is extremelyimportant to the success of the method of applying vitreous enamel toarticles of the character referred to herein. As will be apparent, whenthe article to be coated is provided with a pillowed, uted, ribbed orsimilar ornamental surface, the channels, such as those indicated at.29'in Figs. 1 and 2, existing between the raisedV portions intersect thedepressions 25 so that the tendency may be for the-coating to pull awayfromvthe corner 25 to a greater extent adl.

jacent such arcas. In such event, the flowable enamel may actually drawaway from the adjacent portions of the sharp corner 25 to a degree suchthat the areas adjacent the edge of the panel may be uncoated andseparation or discontinuity of the enamel coating is effected.Consequently, it is highly desirable that the area referred to above bemaintained as small as possible. This is accomplished by making thegrooves or channels 29 between the ornamental raised portions or theflutes, as the case may be. relatively narrow so as to produce laneffective area-of a size which will not cause such abnormal pullingforce. It has been determined that when the Width of the channel 29' ismade approximately twicethat of the depression 26, a continuous andotherwise satisfactory coating is produced.'

It will be apparent that the present method is concerned particularlywith coating panels of a cast fmetal character since the criticaldimensions referred to abovecan best'be attained by afcasting process.However, it is Within-the concept of my invention to provide panelsfabricated from ysheet metal althoughin such case' it is necessary toperform an additional step, that is, to grind the outer surfaces of theflanges so as to avoid rounded corners `at the intersection of theilanges and the substantially planar surfaces of the panels.

Referring now to Fig. 5, the invention further contemplates `theprovision of a panel 58 of alternative construction. In this panel, lthecorner 5l occurring at the intersection `of the planar surface 52 andthe flange 53 is made relatively acute by extending the material in asteep ridge. The inclined sides of the ridge and the surface 52 providebetween them a depression or channel 54 towardl which the' vitreousenamel coating;` is drawn' to form beads. asfsliovm, underthe-iniiuenceof surface tension of the enamel on the ysurface 52 during the firing ofthe-coating-onthe panel. Thus, the coating is prevented from eX- tendingover the edge of the panel onto the flange 53. Consequently, whenithepanels-50 are'secured together in the relation shownin Fig. 5, there isno tendency to damage the protective and ornamental coating of vitreousenamel.

While I have herein described-theimproved enamel coated article asembodied in two forms of construction, and the method of applying theenamel coat as comprising a specific series of steps, it will beapparent that Avarious modica- Itions might be made in this constructionand method Within :the concept of the invention. Consequently, I do notwish to be limited in this respect, but desire to be afforded the fullscope of the appended claims.

I claim as my invention:

1.l In a process of coating a metal article with vitreous enamel whereinsaidv article has a '00p surface and a side edge portion and is adapted.to -be assembled in side-by-side abutting relationship with the sideedge portion of a similar article to form a panel structure and in whichthe top surfaces only are provided with a vitreous enamel coatingwhereby the panel structure has an apparent continuous vitreous surface,the steps of forming said article so that said .top surface merges withsaid side edge portion at an acute angleto form a shallow depressionadjacent said side edge portionand a sharp corner at the junction ofsaid top surface'andv said side-edge portion; applying a vitreous enamelslip to said top surface; firing said article to cause said vitreousenamel to'become flowable; and cooling said article to harden saidvitreous enamel, the merging of said top surface with said side edgeportion at an .acute angle causing said vitreous enamel on firingof saidarticle to recede very slightly from said corner and thus be preventedfrom fiowing over said corner and onto said side edge portion andcausing fracture of said enamel when said article is assembled inabutting relationship with another of said articles. 2. In a process of4coating .a metal article with vitreous enamel, wherein said article hasa top surface and a side edge portion and is adapted to be assembled inside-by-side abutting relationship with the side edge portion of asimilar article to forma panel structure and in `which the top surfacesonly are provided with a vitreous enamel coating whereby the panelstructure .has an apparent continuous vitreous surface, the steps of tforming said article so that said top surface merges with said side edgeportion at an acute` angle to form a depression of a depth less than thethickness of said vitreous enamel ,and asharp corner at the junction ofsaid top surface and said side edge portion; applying a vitreous enamelslip to said top surface; firing said article to cause said vitreousenamel to become ilowable; and cooling said article to harden saidvitreous enamel, the merging of said top surface with said side edgeportion at an acute angle causing lsaid vitreous enamel on firing ofsaid article to recede very slightly from said 'corner and thus beprevented froin flowing over said corner and onto said side edge portionand causing fracture of said enamel when said article is assembled inabutting relationship with another ofV said articles.

3. A fired coated metal article adapted to be assembledA in 1side-by-side abutting relationship with at least one-similar-artlcletoAforma panei structure having an apparent ccntinuous vitreous surface,said article having a top surface and a side edge, said top surfacehaving a shallow depression formed therein including a surface portionmerging with said side edge at an acute angle to form a sharp corner,and a vitreous enamel coating on said top surface extending immediatelyadjacent to but terminating just short of said sharp corner, wherebyfracture of said enamel when said article is assembled in side-by-sideabutting relationship with another of said articles is prevented.

4. An article as called for by claim 3 wherein said depression is of adepth less than the thickness of said coating.

5. An article as called for by claim 3 wherein said depression is of adepth less than the thickness of the marginal edge of said coating.

6. An article as called for by claim 3 wherein said side edge comprisesa flange member disposed at a right angle to the general ,plane of saidtop surface.

10 7. An article as called for by claim 3 wherein said top surface isprovided with a plurality of ornamental projections and in which thewalls of said projections nearest said side edge merge with said 'topsurface portion of said depression.

RALPH BROWN.

REFERENCES CITEE The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. IN A PROCESS OF COATING A METAL ARTICLE WITH VITREOUS ENAMEL WHEREINSAID ARTICLE HAS A TOP SURFACE AND A SIDE EDGE PORTION AND IS ADAPTED TOBE ASSEMBLED IN SIDE-BY-SIDE ABUTTING RELATIONSHIP WITH THE SIDE EDGEPORTION OF A SIMILAR ARTICLE TO FORM A PANEL STRUCTURE AND IN WHICH THETOP SURFACE ONLY ARE PROVIDED WITH A VITREOUS ENAMEL COATING WHEREBY THEPANEL STRUCTURE HAS AN APARENT CONTINUOUS VITREOUS SURFACE, THE STEP OF:FORMING SAID ARTICLES SO THAT SAID TOP SURFACE MERGES WITH SAID SIDEEDGE PORTION AT AN ACUTE ANGLE TO FORM A SHALLOW DEPRESSION ADJACENTSAID SIDE EDGE PORTION AND A SHARP CORNER AT THE JUNCTION OF SAID TOPSURFACE AND SAID SIDE EDGE PORTION; APPLYING A VITREOUS ENAMEL SLIP TOSAID